Conventionally, thin-film chip resistors having resistive elements made of metal thin films have been widely used. A thin-film resistive element used for a thin-film chip resistor is obtained by forming a resistive film through deposition of metal layers of chromium (Cr) and silicon (Si), or nickel (Ni) and chromium (Cr), for example, on a ceramic substrate and alloying them using sputtering or vacuum deposition, and then patterning the film into a desired shape using photolithography or the like. Typically, high-precision chip resistors can be realized using a thin-film technology.
As an example of producing a resistive thin film with high resistivity, there is disclosed a method of sputtering a target containing silicon and also containing transition metal, such as chromium, therein, in a nitrogen-containing gas so as to deposit them on a substrate (see Patent Literature 1). The deposited resistive thin film is patterned into a shape with an approximately desired resistance value using photolithography or the like, which is then subjected to heat treatment under an inert gas atmosphere, such as nitrogen or argon. Optimally setting the heat treatment conditions therefor can suppress the temperature coefficient of resistance (TCR) to a small value of less than or equal to ±25 ppm/° C.
After that, a resist material for forming electrodes on the thin-film resistive pattern is applied to the substrate and the resulting resist film is patterned, and then, copper or the like is deposited as a material of the electrodes of the resistor using sputtering or the like. Then, the resist and copper are partially removed using a lift-off method so that copper electrodes are formed through patterning.
After the electrodes are formed through a patterning process, a silicon oxide film is deposited as a protective film using plasma CVD or the like. Then, the silicon oxide film is patterned through photolithography and etching steps, so that the silicon oxide film in the electrode regions is removed and openings for contact are formed.
Then, an overcoat film that uses resin paste or the like is applied using screen printing or the like, which is then cured. After that, primary heat treatment and a primary breaking process; formation of end-face electrodes; secondary heat treatment and a secondary breaking process; and the like are performed so as to obtain individual chips. Then, the electrodes are plated, for example, to complete a thin-film resistor. For the overcoat film, a resin material is preferably used.
In addition, regarding a thin-film resistor that uses metal oxide, there is disclosed a method of depositing insulating metal oxide with high resistivity on the surface of the thin-film resistor (see Patent Literature 1). Similarly, regarding a thin-film resistor that uses metal nitride such as the one described above, there is also known a method of depositing insulating metal nitride with high resistivity on the surface of the thin-film resistor.